Method for fabricating n-type carbon nanotube device

ABSTRACT

A method for fabricating an n-type carbon nanotube device, characterized in that thermal annealing and plasma-enhanced chemical vapor-phased deposition (PECVD) are employed to form a non-oxide gate layer on a carbon nanotube device. Moreover, the inherently p-type carbon nanotube can be used to fabricate an n-type carbon nanotube device with reliable device characteristics and high manufacturing compatibility.

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention generally relates to a method forfabricating an n-type carbon nanotube device and, more particularly, toa method characterized in that thermal annealing and plasma-enhancedchemical vapor-phased deposition (PECVD) are employed to form anon-oxide gate layer on a carbon nanotube device. Therefore, theinherently p-type carbon nanotube can be used to fabricate an n-typecarbon nanotube device with reliable device characteristics and highmanufacturing compatibility.

[0003] 2. Description of the Prior Art

[0004] In the nanotechnology era, it is an important issue to develop acarbon nanotube (CNT) logic device. Inherently, a carbon nanotubetransistor exhibits p-type characteristics at room temperature.

[0005] Richard Smalley et al. have disclosed a conventional technique in“Chemical doping of individual semiconducting carbon-nanotube ropes”(Physical Review B, Vol.61, No. 16), in which potassium ions areimplanted into the carbon nanotube so as to provide sufficient electronssuch that the carbon nanotube exhibts n-type characteristics. However,this method is not compatible with the state-of-the-art semiconductormanufacturing process.

[0006] Therefore, there is need in providing a method for fabricating ann-type carbon nanotube device, in which the p-type carbon nanotubeexhibits n-type characteristics at room temperature and the method iscompatible with the state-of-the-art semiconductor manufacturingprocess.

SUMMARY OF THE INVENTION

[0007] Accordingly, it is the primary object of the present invention toprovide a method for fabricating an n-type carbon nanotube device,characterized in that thermal annealing and plasma-enhanced chemicalvapor-phased deposition (PECVD) are employed to form a non-oxide gatelayer on a carbon nanotube device.

[0008] It is the secondary object of the present invention to provide amethod for fabricating an n-type carbon nanotube device, characterizedin that the inherently p-type carbon nanotube can be used to fabricatean n-type carbon nanotube device with reliable device characteristicsand high manufacturing compatibility.

[0009] In order to achieve the foregoing objects, the present inventionprovides a method for fabricating an n-type carbon nanotube device,comprising steps of: depositing an oxide film on a substrate; forming afirst metal film on said oxide film; forming a carbon nanotube layer onsaid first metal film; depositing a gate layer covering said first metalfilm and said carbon nanotube layer; and forming a gate electrode onsaid gate layer.

[0010] The present invention further provides another method forfabricating an n-type carbon nanotube device, comprising steps of:forming a gate electrode in a substrate; depositing an oxide film onsaid substrate and said gate electrode; forming a first metal film onsaid oxide film; depositing a carbon nanotube layer on said first metalfilm; and depositing a gate layer covering said first metal film andsaid carbon nanotube layer.

[0011] Other and further features, advantages and benefits of theinvention will become apparent in the following description taken inconjunction with the following drawings. It is to be understood that theforegoing general description and following detailed description areexemplary and explanatory but are not to be restrictive of theinvention. The accompanying drawings are incorporated in and constitutea part of this application and, together with the description, serve toexplain the principles of the invention in general terms.

BRIEF DESCRIPTION OF THE DRAWINGS

[0012] The objects, spirits and advantages of the preferred embodimentsof the present invention will be readily understood by the accompanyingdrawings and detailed descriptions, wherein:

[0013]FIG. 1A is a schematic cross-sectional view showing an oxide filmdeposited on a substrate in accordance with one preferred embodiment ofthe present invention;

[0014]FIG. 1B is a schematic cross-sectional view showing a first metalfilm formed on the oxide film in accordance with one preferredembodiment of the present invention;

[0015]FIG. 1C is a schematic cross-sectional view showing a carbonnanotube layer formed on the first metal film in accordance with onepreferred embodiment of the present invention;

[0016]FIG. 1D is a schematic cross-sectional view showing a gate layercovering the first metal film and the carbon nanotube layer inaccordance with one preferred embodiment of the present invention;

[0017]FIG. 1E is a schematic cross-sectional view showing a second metalfilm formed on the gate layer in accordance with one preferredembodiment of the present invention;

[0018]FIG. 1F is a schematic cross-sectional view showing a gateelectrode formed on the gate layer in accordance with one preferredembodiment of the present invention;

[0019]FIG. 2A is a schematic cross-sectional view showing a gateelectrode formed in a substrate in accordance with another preferredembodiment of the present invention;

[0020]FIG. 2B is a schematic cross-sectional view showing an oxide filmdeposited on the substrate and the gate electrode in accordance withanother preferred embodiment of the present invention;

[0021]FIG. 2C a schematic cross-sectional view showing a first metalfilm covering the oxide film in accordance with another preferredembodiment of the present invention;

[0022]FIG. 2D a schematic cross-sectional view showing a carbon nanotubelayer deposited on the first metal film in accordance with anotherpreferred embodiment of the present invention; and

[0023]FIG. 2E a schematic cross-sectional view showing a gate layercovering the first metal film and the carbon nanotube layer inaccordance with another preferred embodiment of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

[0024] The present invention providing a method for fabricating ann-type carbon nanotube device can be exemplified by the preferredembodiments as described hereinafter.

[0025] The method according to the present invention employsplasma-enhanced chemical vapor-phased deposition (PECVD) to form anon-oxide gate layer, such as silicon nitride (SiNx), on a carbonnanotube device to function as a gate oxide layer. Meanwhile, thermalannealing is performed to fabricate an n-type carbon nanotube devicefrom a p-type carbon nanotube.

[0026] Please refer to FIG. 1A to FIG. 1F, which show a method forfabricating an n-type carbon nanotube device in accordance with onepreferred embodiment of the present invention. As shown in FIG. 1A, anoxide film 11 of 1000 Å in thickness is deposited on a substrate 10.Then, a first metal film 12 is formed on the oxide film 11. In thepresent embodiment, the first metal film 12 is formed of Ti. The firstmetal film 12 is then patterned by photolithography as well as etchingso as to function as a drain region and a source region, as shown inFIG. 1B.

[0027] As shown in FIG. 1C, a carbon nanotube layer 13 formed byspin-coating carbon nanotube dimethylformamide (CNT DMF) on the firstmetal film 12. The carbon nanotube layer 13 conducts the current betweenthe drain and the source in a transistor.

[0028] In FIG. 1D, a gate layer 14 is formed by plasma-enhanced chemicalvapor-phased deposition (PECVD) and thermal annealing at 400° C. tocover the first metal film 12 and the carbon nanotube layer 13. The gatelayer 14 is formed of a non-oxide material, such as silicon nitride(SiNx) in the present embodiment. By using the gate layer 14 as a gateoxide layer, the inherently p-type carbon nanotube device exhibitsn-type characteristics. Later, as shown in FIG. 1E, a second metal film15 of 1500 Å in thickness is deposited on the gate layer 14. In thepresent embodiment, the second metal film 15 is formed of Ti.

[0029] Finally, the second metal film 15 is patterned to form a gateelectrode 16 for an n-type carbon nanotube device by using conventionalsemiconductor manufacturing process such as photolithography andetching, as shown in FIG. 1F.

[0030] For another embodiment of the present invention, please refer toFIG. 2A to FIG. 2E, which show a method for fabricating an n-type carbonnanotube device. As shown in FIG. 2A, a substrate 10 is patterned byetching to form a pattern for the gate electrode and then a metal filmis formed in the substrate 10 by sputtering so as to form a gateelectrode 20. Later, as shown in FIG. 2B, an oxide film 11 of 1000 Å inthickness is deposited on the substrate 10 and the gate electrode 20. Afirst metal 12 is then sputtered onto the oxide film 11. In the presentembodiment, the first metal is formed of Ti. The first metal film 12 isthen patterned by photolithography as well as etching so as to functionas a drain region and a source region, as shown in FIG. 2C.

[0031] In FIG. 2D, a carbon nanotube layer 13 formed by spin-coatingcarbon nanotube dimethylformamide (CNT DMF) on the first metal film 12.The carbon nanotube layer 13 conducts the current between the drain andthe source in the n-type carbon nanotube device according to the presentinvention.

[0032] Finally, as shown in FIG. 2E, a gate layer 14 is formed byplasma-enhanced chemical vapor-phased deposition (PECVD) and thermalannealing at 400° C. to cover the first metal film 12 and the carbonnanotube layer 13. The gate layer 14 is formed of a non-oxide material,such as silicon nitride (SiNx) in the present embodiment. By using thegate layer 14 as a gate oxide layer, the inherently p-type carbonnanotube device exhibits n-type characteristics.

[0033] According to the above discussion, it is apparent that thepresent invention discloses a method for fabricating an n-type carbonnanotube device, characterized in that thermal annealing andplasma-enhanced chemical vapor-phased deposition (PECVD) are employed toform a non-oxide gate layer on a carbon nanotube device. Therefore, theinherently p-type carbon nanotube can be used to fabricate an n-typecarbon nanotube device with reliable device characteristics and highmanufacturing compatibility. Therefore, the present invention has beenexamined to be progressive, advantageous and applicable to the industry.

[0034] Although this invention has been disclosed and illustrated withreference to particular embodiments, the principles involved aresusceptible for use in numerous other embodiments that will be apparentto persons skilled in the art. This invention is, therefore, to belimited only as indicated by the scope of the appended claims.

What is claimed is
 1. A method for fabricating an n-type carbon nanotubedevice, comprising steps of: depositing an oxide film on a substrate;forming a first metal film on said oxide film; forming a carbon nanotubelayer on said first metal film; depositing a gate layer covering saidfirst metal film and said carbon nanotube layer; and forming a gateelectrode on said gate layer.
 2. The method for fabricating an n-typecarbon nanotube device as claimed in claim 1, wherein said first metalfilm is formed by sputtering and and is patterned by etching.
 3. Themethod for fabricating an n-type carbon nanotube device as claimed inclaim 1, wherein a drain electrode and a source electrode of said carbonnanotube device are formed on said first metal film.
 4. The method forfabricating an n-type carbon nanotube device as claimed in claim 1,wherein said carbon nanotube layer is formed by spin-coating carbonnanotube dimethylformamide (CNT DMF) on said first metal film.
 5. Themethod for fabricating an n-type carbon nanotube device as claimed inclaim 1, wherein said gate layer is formed of a non-oxide material. 6.The method for fabricating an n-type carbon nanotube device as claimedin claim 1, wherein said gate layer is formed by using plasma-enhancedchemical vapor-phased deposition (PECVD).
 7. The method for fabricatingan n-type carbon nanotube device as claimed in claim 1, wherein saidgate electrode is formed by sputtering and etching a second metal film;8. The method for fabricating an n-type, carbon nanotube device asclaimed in claim 1, wherein said n-type carbon nanotube device isvacuum-annealed after said gate electrode is formed.
 9. A method forfabricating an n-type carbon nanotube device, comprising steps of:forming a gate electrode in a substrate; depositing an oxide film onsaid substrate and said gate electrode; forming a first metal film onsaid oxide film; depositing a carbon nanotube layer on said first metalfilm; and depositing a gate layer covering said first metal film andsaid carbon nanotube layer.
 10. The method for fabricating an n-typecarbon nanotube device as claimed in claim 9, wherein said gateelectrode is formed by sputtering a metal film onto an etched substrate.11. The method for fabricating an n-type carbon nanotube device asclaimed in claim 9, wherein said first metal film is formed bysputtering and and is patterned by etching.
 12. The method forfabricating an n-type carbon nanotube device as claimed in claim 9,wherein said carbon nanotube layer is formed by spin-coating carbonnanotube dimethylformamide (CNT DMF) on said first metal film.
 13. Themethod for fabricating an n-type carbon nanotube device as claimed inclaim 9, wherein said gate layer is formed of a non-oxide material. 14.The method for fabricating an n-type carbon nanotube device as claimedin claim 9, wherein said gate layer is formed by using plasma-enhancedchemical vapor-phased deposition (PECVD) and vacuum-annealing.